4 ms·

The spin was not visible to these pilots presumably because it was happening in small increments with a delay between them.

acqq 8y ago
Exactly. It was not "runaway" in the sense of "continuously doing the same." Something was happening, from the point of view of the pilot and co-pilot "at random." (Not to mention that on the previous models exactly such pattern was effectively impossible to happen). The faulty non-redundant sensor was producing false reading and that was the input to the to the pilots completely unknown MCAS which then moved the nose down based on the difference between the input and MCAS' expected target, turning "the correction" on only from time to time. The presence of the third, off-duty pilot on the flight before additionally explains even better how in that case the crash was avoided. While the pilot and co-pilot were at the controls, the third one, looking from behind, didn't have the direct duties to do, so he had enough time to both just observe everything that was going on and the less immediate stress to allow him to come to the solution that worked. Like when one programmer spends half an hour on something "not working" and complains to the colleague who just takes a look and immediately sees what the first one hasn't for half an hour. Additionally the movement of the trim wheel is actually easier to follow from the place in the back (see https://news.ycombinator.com/item?id=19440045 https://news.ycombinator.com/item?id=19440045 ). And there's also a possibility that the false sensor reading and MCAS together produced a slightly different differential signal which resulted in more obvious manifestation of the problem. Possibly both elements contributed to the lucky outcome in that previous flight. In the old times of civil aviation there was the third person on duty in the cockpit, the "flight-engineer." As the planes got more computerized controls, they started to be certified to fly with two-pilot crews. The computerized systems, when working, do reduce the chance of the crash and overall number of accidents did decrease simply because the humans were on the average less often in control, and therefore there was less chance to do anything wrong. The problem is when the unreported computerized controls secretly depend on the single sensor that can be faulty. And when they actively confuse the pilot and ruin the flight instead of helping him.
- kayfox 8y ago
  "Runaway" in the sense of "its moving in a undesired and unexpected direction and continues to do so despite attempts to stop it".
  - jeremysmyth 8y ago
    "Runaway" is a term of art here. Redefining it for this conversation is unhelpful.
ahoka 8y ago
If anyone wonders this is how it looks like: https://youtu.be/-X01uY0bJs0?t=48 https://youtu.be/-X01uY0bJs0?t=48
- TheSpiceIsLife 8y ago
  And sounds? The trim wheels moving also makes a sound?
  - deleted 8y ago
    [deleted]
  - ekianjo 8y ago
    From the videos I have seen in cockpit it does seem to make a sound as it rolls.
  - WalterBright 8y ago
    Yes. The ratcheting sound is deliberate, so the pilots don't need to see the wheels spin to know the trim is running. Also note that there's a white stripe on the wheel so it's easy to see it is running.
    - jacobush 8y ago
      Someone else in the thread said newer models don't make a sound.
  - michaelt 8y ago
    You'll note in that video, the left-hand pilot has a headset on, presumably the right-hand pilot does too. Headsets are seen in other videos [1] of the cockpit. So even if the spinning trim wheels make noise, they may not have heard it. (My google image search shows some pilots wearing two-ear headsets, some wearing one-ear headsets, some wearing two-ear headsets with side not on their ear, and some not wearing headsets. But some of those are pilots posing for photos, and presumably pilots don't let people visit the cockpit during critical stages of the flight) [1] https://youtu.be/wz2Q3COfveg?t=409 https://youtu.be/wz2Q3COfveg?t=409

acqq 8y ago

Exactly. It was not "runaway" in the sense of "continuously doing the same." Something was happening, from the point of view of the pilot and co-pilot "at random." (Not to mention that on the previous models exactly such pattern was effectively impossible to happen). The faulty non-redundant sensor was producing false reading and that was the input to the to the pilots completely unknown MCAS which then moved the nose down based on the difference between the input and MCAS' expected target, turning "the correction" on only from time to time. The presence of the third, off-duty pilot on the flight before additionally explains even better how in that case the crash was avoided. While the pilot and co-pilot were at the controls, the third one, looking from behind, didn't have the direct duties to do, so he had enough time to both just observe everything that was going on and the less immediate stress to allow him to come to the solution that worked. Like when one programmer spends half an hour on something "not working" and complains to the colleague who just takes a look and immediately sees what the first one hasn't for half an hour. Additionally the movement of the trim wheel is actually easier to follow from the place in the back (see https://news.ycombinator.com/item?id=19440045 https://news.ycombinator.com/item?id=19440045 ). And there's also a possibility that the false sensor reading and MCAS together produced a slightly different differential signal which resulted in more obvious manifestation of the problem. Possibly both elements contributed to the lucky outcome in that previous flight. In the old times of civil aviation there was the third person on duty in the cockpit, the "flight-engineer." As the planes got more computerized controls, they started to be certified to fly with two-pilot crews. The computerized systems, when working, do reduce the chance of the crash and overall number of accidents did decrease simply because the humans were on the average less often in control, and therefore there was less chance to do anything wrong. The problem is when the unreported computerized controls secretly depend on the single sensor that can be faulty. And when they actively confuse the pilot and ruin the flight instead of helping him.

kayfox 8y ago
"Runaway" in the sense of "its moving in a undesired and unexpected direction and continues to do so despite attempts to stop it".
- jeremysmyth 8y ago
  "Runaway" is a term of art here. Redefining it for this conversation is unhelpful.

ahoka 8y ago

If anyone wonders this is how it looks like: https://youtu.be/-X01uY0bJs0?t=48 https://youtu.be/-X01uY0bJs0?t=48

TheSpiceIsLife 8y ago
And sounds? The trim wheels moving also makes a sound?
- deleted 8y ago
  [deleted]
- ekianjo 8y ago
  From the videos I have seen in cockpit it does seem to make a sound as it rolls.
- WalterBright 8y ago
  Yes. The ratcheting sound is deliberate, so the pilots don't need to see the wheels spin to know the trim is running. Also note that there's a white stripe on the wheel so it's easy to see it is running.
  - jacobush 8y ago
    Someone else in the thread said newer models don't make a sound.
- michaelt 8y ago
  You'll note in that video, the left-hand pilot has a headset on, presumably the right-hand pilot does too. Headsets are seen in other videos [1] of the cockpit. So even if the spinning trim wheels make noise, they may not have heard it. (My google image search shows some pilots wearing two-ear headsets, some wearing one-ear headsets, some wearing two-ear headsets with side not on their ear, and some not wearing headsets. But some of those are pilots posing for photos, and presumably pilots don't let people visit the cockpit during critical stages of the flight) [1] https://youtu.be/wz2Q3COfveg?t=409 https://youtu.be/wz2Q3COfveg?t=409